A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the patent and trademark office, patent file or records, but otherwise reserves all copyright rights whatsoever.
This application is submitted with a computer program listing appendix containing copyrighted material, copyright 1996, National Semiconductor Corporation. Such appendix consists of a compact disc containing 3 electronic files with respective sizes of 2716, 2911 and 2703 kilobytes.
1. Field of the Invention
The present invention relates to data receivers for receiving high data rate signals from long lengths of cable, and in particular, data receivers for receiving high data rate, binary or MLT3 encoded data signals from long lengths of cable, while providing signal baseline restoration, adaptive signal equalization and dynamic data signal slicing.
2. Description of the Related Art
Recovering data which has been transmitted over a long length of cable at high rates requires that such data be equalized in order to compensate for the loss and phase dispersion of the cable. Further, in those applications where the cable length may vary, such equalization must be based upon a complementary transfer function which is capable of adapting accordingly since the transfer function of the cable varies with the length of the cable. This type of data recovery is generally done using three functions: a filter function; a dc restoration and slicing function; and an adaptation control, or servo, function.
The filter function is performed using a complementary (with respect to the complex cable loss characteristic) filter which synthesizes the inverse of the transfer function of the cable. Since the bit error rate (BER) is directly related to jitter, an important performance metric for an equalizer is jitter within the output waveform. The extent to which the equalizer is able to match the inverse of the complex cable loss characteristic determines the extent to which inter-symbol interference induced jitter is eliminated.
The dc restoration function is necessary to ensure that the equalized incoming signal is properly centered within the dynamic range of the data recovery system so as to allow for accurate signal slicing. The slicing function is used to extract the data from the equalized signal.
The adaptation control, or servo, function is necessary to ensure that the data recovery system is able to adapt to changes in the incoming data signal, such as increases and decreases in signal amplitude and changes in signal phase, as well as changes in the operating environment.
In accordance with one embodiment of the present invention, a control loop for controlling a multilevel detecting of an input data signal includes a data signal peak detection circuit, a signal processing circuit and a peak reference generation circuit. The data signal peak detection circuit is configured to receive a plurality of peak reference signals and in accordance therewith receive and detect an input data signal and in accordance therewith provide a plurality of peak parameter signals which indicates whether the input data signal has transcended a plurality of predetermined signal levels including predetermined minimum and maximum signal levels. The signal processing circuit is coupled to the data signal peak detection circuit and is configured to receive and process the plurality of peak parameter signals and in accordance therewith provide: a first processed parameter signal which indicates whether the input data signal has transcended one of the predetermined minimum and maximum signal levels; and a second processed parameter signal which indicates which one of the predetermined minimum and maximum signal levels the input data signal has transcended. The peak reference generation circuit is coupled to the signal processing circuit and the data signal peak detection circuit and is configured to receive and process the first and second processed parameter signals and in accordance therewith provide the plurality of peak reference signals.
In accordance with another embodiment of the present invention, a method of controlling a multilevel detecting of an input data signal with a control loop includes the steps of:
receiving a plurality of peak reference signals and in accordance therewith receiving and detecting an input data signal and in accordance therewith generating a plurality of peak parameter signals which indicates whether the input data signal has transcended a plurality of predetermined signal levels including predetermined minimum and maximum signal levels;
processing the plurality of peak parameter signals and in accordance therewith generating
a first processed parameter signal which indicates whether the input data signal has transcended one of the predetermined minimum and maximum signal levels, and
a second processed parameter signal which indicates which one of the predetermined minimum and maximum signal levels the input data signal has transcended; and
processing the first and second processed parameter signals and in accordance therewith generating the plurality of peak reference signals.
These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.